The present invention relates to a method of recovering a heavy metal and a reagent for recovery of a heavy metal for use in the same.
It is known that heavy metals such as mercury, cadmium, and lead are accumulated in human bodies, resulting in adverse effects on health. Therefore, it is important to analyze heavy metals in biological samples such as urine and the like and samples of food and beverage such as water and the like.
In analysis of a heavy metal, generally, as a pretreatment, foreign substances are removed from a sample, and a heavy metal is separated from the resultant sample. Then, the separated heavy metal is analyzed. As the pretreatment, a solvent extraction is widely used. The solvent extraction is a method in which a heavy metal in a sample is extracted in an organic medium, utilizing the polarity of a chelating agent to be bound to the heavy metal, according to the difference between the distribution coefficient of the chelating agent to an aqueous medium and that to the organic medium. The heavy metal can be further concentrated by evaporating the organic medium after the extraction. As a specific example of the solvent extraction, a dithizone method using, as the chelating agent, 1,5-diphenyl-3-thiocarbazone (hereinafter, also referred to as “dithizone”) that is insoluble in an aqueous medium under acidic conditions is defined in JIS, for example (see, Mercury Analysis Manual, Ministry of the Environment, March 2004, Japanese Patent No. 2969226). In the dithizone method, first, dithizone and a liquid sample such as urine are mixed under acidic conditions, and thus, in the mixture thus obtained, a complex between the dithizone and a heavy metal being in the liquid sample is formed. Subsequently, an organic medium such as carbon tetrachloride or chloroform is added to the mixture. Then, the complex is extracted in the organic medium because the distribution coefficient of the complex to the aqueous medium is different from that of the complex to the organic medium. Thereafter, this organic medium is recovered. Thus, the heavy metal is recovered as the complex from the liquid sample. When the organic medium is evaporated, the heavy metal can be further concentrated.
However, the inventors of the present invention found a problem in that the recovery rates vary among samples when heavy metals are recovered by such a method even though the samples are treated under the same conditions. The variation in recovery rate among samples could lead to insufficient reliability of results obtained by quantitatively determining recovered heavy metals.